The invention relates to a process and device for the reduced-pressure refining of a glass melt using a reduced-pressure apparatus, in which the glass melt is fed to a refining bank via a riser and is discharged again from the refining bank via a downpipe, a reduced pressure being generated by means of the glass flow in the refining bank.
The refining of the glass melt, i.e. the removal of gas bubbles from the glass melt, is used to eliminate bubbles. With small crucible melts, the rise of the gas bubbles out of the glass melt has already been accelerated by means of the application of a reduced pressure above the glass melt.
Devices for reduced-pressure refining of a glass melt using a reduced-pressure apparatus of the type mentioned in the introduction are known, for example, from documents U.S. Pat. No. 1,598,308, EP 0 908 417 A2 and JP 2-2211229 A. The first two of these documents disclose the use of ceramic refractory materials as glass-contact material, while the last of these documents discloses the use of platinum or platinum alloys as glass-contact material.
Both the use of ceramic refractory materials and the use of platinum and its alloys are associated with a range of drawbacks.
For example, ceramic refractory materials, when in contact with a glass melt, are subject to considerable wear and increased corrosion compared to platinum and its alloys. This entails firstly short plant operating times and a high outlay on maintenance and repair and secondly a high potential for the formation of glass defects (formation of cords, inclusions, bubbles in particular in the downpipe). Furthermore, heating presents problems for glass melts which cannot be heated directly by electrical means or can only be heated in this way with difficulty.
With regard to the formation of glass defects, it is preferable to use platinum or platinum alloys, but the capital costs which this incurs are very high.